John Whaite's perfect roasties

For my potatoes I boil them in well-salted water for 20 minutes, then drain and spread out onto a tray to cool. Then I preheat a baking tray at 200/180 fan with a generous dollop of goose fat and 3 tbsp of rapeseed oil. After 10 minutes I add the potatoes and roast them for 45-60 minutes until very golden brown.